Abstract 061
The relationships between instrumental and human visual perception of
turbidity in clear and colored samples simulating wines and grape juices
Proceedings, 4th International Cool Climate Symposium on Viticulture and Enology Rochester, NY, 1996, pp. VII-9 – VII-12
A. Carrasco and K.J. Siebert
A number of physical factors including particle diameter, wavelength of light and the angle to the incident beam at which scattering is observed are known to influence instrumental measurements of light scattering. Relatively little is known about how these factors influence human perceptions of turbidity. Colored samples offer additional complications as absorbance can cause underestimation of the amount of scattering and shift the effective wavelength used for observation. Synthetic beads of several known sizes were used singly or in combination to prepare artificial colloidal suspensions of known concentration and composition. Some of these samples were colored with red and yellow food coloring to duplicate the color range spanned by wines and grape juices. The resulting mixtures were measured with a light scattering instrument using transmission, narrow angle, right angle, and back scatter detectors. Observations were also made in the ratio turbidimeter mode. The same samples were viewed by human panelists. Thresholds were determined by ASTM Method E-679, the Ascending Method of Limits. A vocabulary describing appearance and intensity of haze was developed and used in Quantitative Descriptive Analysis (QDA). Sensory data obtained by Magnitude Estimation were correlated with the instrumental measurements. The results were used to develop mathematical models describing the relationships between the sample composition and each of the instrumental perceptions, between the sample properties and visual perception results and between instrumental and human visual perception.
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